This invention pertains generally to the art of transport refrigeration units and in particular to that part of the art relating to such units adapted for use on freight containers which may be transported by truck, train or ship.
A refrigeration unit according to our invention has various features believed to be superior to prior art units used in the same type of service. While some of these features have been available individually with particular prior art units, no prior art units of which we are aware has all of these features available in one package
As background for better understanding the desirability of some of these features, a brief discussion of the type of service to which sea-going refrigeration freight containers are subject, and the relationship of this service to the refrigeration unit, is considered in order.
These freight containers are in the form of large, thermally insulated boxes which may be stacked on the deck of container ships for ocean travel, and may be transferred thereto or therefrom to a train flat car, or a truck trailer chassis for land transport. Because of such handling, such containers are typically constructed with a pocket or recess at the front of the container to receive the refrigeration unit, which should fit within the pocket without projecting beyond it, thereby to avoid damage to the refrigeration unit in handling of the freight container. To provide flexibility in the transport mode (ship, train, truck) it is desirable that the refrigeration unit be adapted to be powered either electrically, or by an internal combustion engine. Since not only the refrigeration compressor requires power, but also means must be provided to drive evaporator and condenser fans, it is considered desirable if possible to use motors to drive these fans to avoid maintenance problems experienced with fan belt drives that are driven from the prime mover.
Continuing with the characteristics desirable in such a refrigeration unit, obviously the unit should have adequate refrigeration (and heating) capacity to maintain the proper temperature in the container, regardless of whether the container is being transported through desert heat or is in some more moderate climate. Since the container may be transported on deck of ships, which may encounter heavy seas at times, then it should also be constructed in a manner that is not likely to fail under such conditions. At the same time, since most man-made objects are subject to failure, the arrangement and construction of the unit should be such that service upon it is not unduly difficult, even though it may be at the top of a stack of container units aboard a ship encountering heavy weather. Finally, another important consideration is that the container owner desires that the refrigeration unit take up as little internal space in the container as possible so as to maximize the available cargo space.
It will be appreciated by those familiar with the refrigerated container art that these considerations, along with others not here mentioned, are not all easily obtained in a single unit, since some of these considerations and desirable characteristics impact upon each other. In other words, certain features may be available only at the expense of other desirable features. However, we believe that a unit according to our invention yields a reasonably good balance of the major ones of the desirable characteristics, and is a unit eminently suited for its intended service on a refrigerated container.